The present invention relates to a reference voltage generation circuit, a display driver, an electro-optical device, and an electronic instrument.
An electro-optical device represented by a liquid crystal display (LCD) panel has been widely provided in a portable electronic instrument. On the other hand, the electro-optical device is required to display an image rich in color tone by increasing the number of grayscales.
An image signal for displaying an image is generally gamma-corrected corresponding to the display characteristics of a display device. In an electro-optical device, a reference voltage corresponding to grayscale data which determines a grayscale value is selected from a plurality of reference voltages, and the pixel transmissivity is changed based on the selected reference voltage. Therefore, gamma correction is realized by changing the voltage level of each reference voltage.
The reference voltage is generated by dividing the voltage across a ladder resistor circuit by using resistor elements of the ladder resistor circuit, as disclosed in JP-A-2003-233354, JP-A-2003-233355, JP-A-2003-233356, and JP-A-2003-233357. Therefore, the voltage level of each reference voltage can be changed by changing the resistance of each resistor element.
However, more accurate gamma correction may be required along with an increase in resolution and diversification of an LCD panel. In this case, it is difficult to generate the reference voltage with high accuracy merely by changing the resistance of each resistor element of the ladder resistor circuit. In particular, it is difficult to generate a highly accurate reference voltage corresponding to the LCD panel by using a simple configuration when the type of LCD panel is changed. Therefore, control and the configuration for realizing different types of gamma correction become complicated.
However, the voltage level of the reference voltage to be corrected by gamma correction may differ depending on whether the LCD panel is a reflective type or a transparent type, or different colors may be preferred depending on the region in which the LCD panel is used. Or, when driving the LCD panel by using a polarity inversion drive method, the reference voltages used in a positive drive period cannot be directly used as the reference voltages used in a negative drive period when it is desired to increase the resolution.
Gamma correction data for controlling gamma correction may be set in a reference voltage generation circuit. However, as the number of bits of gamma correction data is increased along with an increase in the number of grayscale levels, the time required to set the gamma correction data may be increased, or power consumption required when setting the gamma correction data may be increased. Therefore, it is desirable that the gamma correction data be set at low power consumption even when the number of bits of gamma correction data is increased.